Mass loss of B1 Ia-O supergiants.

Summary. Extensive high dispersion spectroscopic observations of the four luminous B 1 supergiants (bobmetric maguitudes between -9 and -11) HD 152236, HD 169454, BD 1405037, and HDE 269700 have been carried out between 1972 and 1975. All stars show P Cygui line profiles of Ha, H and He 1 5876 and sometimes H . The P Cygni profiles are variable with time. The photospheric lines of all four stars show radial velocity variations (up to 30 km s in the case of HD 152236). From the Ha P Cygni profiles we derived mass loss rates using a method proposed by Hearn (1975). The Ha P Cygni lines of these objects are formed in expanding shells (expansion velocity -150 to -200 km ) at a distance from the stars of about five times the photospheric stellar radius. The mean electron density in the shell is ne 5 1 0 cm - 3 and the average mass loss rates are in the order of 2.0 10-6 . The observed intensity and profile variations of Ha are interpreted in terms of density fluctuations in the shell. The implied mass loss variations are as high as a factor of two and seem to occur within time intervals of days. The observed stellar parameters are compared with theoretical evolutionary tracks calculated on the assumption of mass loss by stellar winds. It is suggested that these very luminous early B supergiants are the progenitors of the Hubble-Sandage variables. Key words: B supergiants - mass loss - radial velocity variations - evolution of massive stars